Fluoroelastomers are a class of high-performance materials with a diverse range of applications encompassing O-rings, valve stem seals, shaft seals, gaskets and hoses in chemical processing industry (CPI).
It is also understood that properties of final vulcanized parts made from fluoroelastomers are greatly influenced by the curing system employed, with peroxide-based curing being considered as delivering higher performances over bis-phenol-based ionic curing.
In peroxide-based curing, a peroxide is added to the fluoroelastomer comprising, either as pendant groups in recurring units of the main chain, or as end-groups, certain cure sites able to react under radical condition, and to a polyfunctional unsaturated compound. Under the effect of heat, the peroxide generates radicals which promote reactions of the fluoroelastomer chain, activated through the cure sites, with the polyfunctional unsaturated compound for yielding a cured mass, with chemically interconnected polymer chains.
Nevertheless, achieving high thermal rating remains a challenging target, even when using peroxide-based formulations.
In this field there is hence a continuous quest for fluoroelastomer curable blends offering an advantageous balance of properties, and more specifically high thermal stability and outstanding steam resistance, and which are easily accessible at reasonable costs.
WO 95/02634 (E.I. DUPONT DE NEMOURS AND COMPANY) 26 Jan. 1995 discloses fluoroelastomer compositions with low concentrations of extractable metal species. The fluoroelastomer may be a perfluoroelastomer or a vinylidene-fluoride-based fluoroelastomer; the compounds is cured by peroxidic route, combining the same with an organic peroxide, a co-agent and an organic acid acceptor, which may be, inter alia, octadecyl amine. Examples 5 and 6 pertains to a peroxide-curable compound based on a copolymer having a composition of 38% perfluoromethylvinylether, 35% vinylidene fluoride, 26% tetrafluoroethylene, 1% 4-bromotrifluoro-3,3,4,4-tetrafluorobutene, and iodine, further compounded with 0.5 phr of octadecylamine. Example 7 pertains to a peroxide-curable compound based on a copolymer having a composition of 50% vinylidene fluoride, 29% hexafluoropropylene, 20% tetrafluoroethylene, 0.6% 4-bromotrifluoro-3,3,4,4-tetrafluorobutene, and 0.2% iodine, further compounded with 0.5 phr of octadecylamine. In all these examples, the fluoroelastomers used comprise a significant amount of recurring units derived from vinylidene fluoride, so that sensitivity to bases at high temperature is the predominant phenomenon, preventing amines to positively influence thermal rating.
WO 2012/049093 (SOLVAY SPECIALTY POLYMERS ITALY, S.P.A.) 19 Apr. 2012 discloses iodine-containing VDF/HFP/TFE fluorelastomeric copolymers comprising at least 35% moles of recurring units derived from VDF, which are cured via peroxidic route, and which may be combined in curable compounds with acid acceptors like notably 1,8-dimethylaminonaphthalene and octadecylamine.